The canonical Wnt signaling pathway is well documented to be pathogenic in a variety of cancers. We hypothesize that this pathway is also at work in B cell-chronic lymphocytic leukemia (B-CLL). In preliminary studies we have identified a number of factors that suggest a functional relevance of the Wnt signaling pathway in B-CLL biology. The studies we propose would demonstrate mechanistically and functionally the relevance of this pathway in B-CLL and identify the therapuetic potential in blocking the pathway in this disease. To understand how the Wnt pathway functions in B-CLL, we will conduct research for the following Aims: 1) We will identify the mechanism(s) of Wnt pathway activation in B-CLL. We will use Wnt qPCR arrays, western blotting, flow cytometry and confocal microscopy to fully characterize the Wnt pathway and its signaling intermediates in leukemic B cells. 2) Test the hypothesis that the p-catenin/LEF-1 complex is activated and critical for CLL B cell survival. We will characterize Wnt transcription factor activation using TOP/Flash luciferase assay and confocal microscopy. To determine the effect on leukemic survival we will use a small molecule inhibitor of the Wnt pathway and siRNA mediated knockdown of Wnt transcription factors. 3) Test the hypothesis that the p-catenin/LEF-1 complex is a key transcriptional regulator of oncogenic genes. We will use chromatin immunoprecipitation (ChIP) and microarray analysis to identify genes regulated by this pathway. Through these studies, we aim to add novel insight into the etiology of this disease and are optimistic that this information can be used to devise timely novel therapeutic interventions. B cell chronic lymphocytic leukemia is a very common leukemia in this country and is currently incurable. Because at least 70 percent of all patients will ultimately require treatment in order to have an enhanced quality of life and increased survival, we are committed to better understanding the underlying mechanisms that contribute to leukemic cell growth and survival. This proposal will take a comprehensive approach to define the role of the Wnt signaling pathway in determining the behavior of the malignant B cells and how this in turn dictates patient clinical outcome.